Torque and angle of rotation detection system

The invention relates to a torque and angle of rotation detection system that includes a rotor unit, a stator unit and strain gauges.

Industrial measurement technology serves to detect physical parameters such as a torque, angle of rotation and the like of industrially manufactured products. For example, test stand technology is used for measuring the torque and angle of rotation of rotating components such as internal combustion engines, electric motors, gearboxes, pumps, and the like. In addition, the torque and angle of rotation of rotating components is also measured in chip removing machining of workpieces.

A system for detecting torque and angle of rotation known as KiTorq and documented in the data sheet 4550A_000-880d-08.20 is available from the applicant. KiTorq is considered as prior art for the purposes of the present invention. KiTorq features a rotor unit and a stator unit. The rotor unit is designed as a flange which can be attached to any rotating component via a screw connection. The rotor unit is configured for rotational speeds of up to 20000 min-. The stator unit, on the other hand, is stationary. It is separated from the rotor unit with respect to an axis of rotation by a radial air gap.

The rotor unit comprises strain gauges. The strain gauges comprise a measuring grid and a bridge circuit. When an electrical voltage is applied to the measuring grid, the measuring grid exhibits an electrical resistance. The electrical resistance changes upon expansion or compression of the measuring grid, which change in electrical resistance generates measurement signals in the bridge circuit. In this way, the strain gauges detect the torque that acts onto the rotor unit. The strain gauges detect the torque in a dynamic manner generating up to 10,000 measurement signals per second with a sampling rate of up to 35 kSample. The measurement signals have a resolution of 24 bit.

The rotor unit comprises a plurality of dipole magnets which are spaced apart from each other. The stator unit comprises a magnetic field sensor that measures the magnetic fields of the dipole magnets during rotation of the rotor unit. The system counts the magnetic fields measured, and since the distance between the dipole magnets is known, determines the angle of rotation traveled by the rotor unit therefrom.

The rotor unit comprises a rotor antenna and the stator unit comprises a stator antenna for the transmission of the measurement signals from the rotor unit to the stator unit. Transmission of the measurement signals occurs in a contactless manner by the rotor antenna sending the measurement signals to the stator antenna. The transmission frequency of 13.56 MHz in the Industrial Scientific and Medical (ISM) band is used for this purpose, and a data transmission rate of up to 1.4 Mbitsecis achieved.

For the operation of the strain gauges and the rotor antenna, the rotor unit must be supplied with electrical power. The stator unit comprises a primary coil, and the rotor unit comprises a secondary coil for this purpose. The primary and secondary coils are inductively coupled to one another. A primary electrical voltage in the primary coil generates a secondary electrical voltage in the secondary coil. Inductive coupling of the primary and secondary coils occurs in a contactless manner in the ISM band with carrier frequencies in the range of 115 kHz to 130 kHz.

The dipole magnets consist of a magnetized mixture of ferrite powder/rubber. With less than 200 mT, the remanence of the dipole magnets is relatively weak. A remanence being that weak is easily disturbed by external magnetic fields which may, thus, falsify the determination of the angle of rotation.

To achieve inductive coupling, the secondary coil comprises an iron powder/resin mixture. The iron powder/resin mixture can be mixed quickly and applied easily to the rotor unit in a curved shape using a spatula where it rapidly hardens. In particular, the same iron powder/resin mixture may be used for rotor units having different radii of curvature. Thus, the use of the iron powder/resin mixture leads to cost-effective production with high variability. However, the freshly mixed iron powder/resin mixture contains air inclusions, which persist even until after the iron powder/resin mixture has cured and result in a low magnetic permeability. As a consequence, the inductive coupling between the primary coil and the secondary coil has a low efficiency.

For the reasons mentioned above, the dipole magnets and the magnetic field sensor as well as the primary and secondary coils must be arranged in close proximity to each other. The radial air gap between the stator unit and the rotor unit is only 1.0 mm in width and must comply with a tight tolerance range for the radial air gap of +/−0.5 mm. To comply with this narrow tolerance range for the radial air gap, the rotor unit is manufactured with a balance quality grade of G.according to DIN ISO 1940-1, which, however, makes the production of KiTorq complex and expensive.

In many cases, after the rotor unit has been attached to a rotating component, there is not enough space in the vicinity of the rotating component for mounting the stator unit adjacent to the rotor unit to arrange the magnetic field sensor in close proximity to the dipole magnets. However, the greater the distance between the magnetic field sensor and the dipole magnets is, then the more error-prone is the measurement of the magnetic fields of the dipole magnets by the magnetic field sensor so that the determination of the angle of rotation may be falsified.

It is a first object of the present invention to provide a torque and angle of rotation detection system comprising a rotor unit and a stator unit that are separated from one another by a radial air gap with respect to an axis of rotation. The air gap desirably is wider than that known from the prior art according to KiTorq and desirably has a broader tolerance range regarding its width than the prior art according to KiTorq.

It is a second object of the invention to suggest a torque and angle of rotation detection system for which the detection of the angle of rotation is not readily disturbed by external magnetic fields.

Furthermore, it is a third object of the invention to provide a torque and angle of rotation detection system that is less expensive to manufacture than the prior art according to KiTorq.

A fourth object of the present invention is to provide a torque and angle of rotation detection system in which the stator unit can be easily and quickly mounted adjacent to the rotor unit to arrange the magnetic field sensor in close proximity to the dipole magnets.

Each of these objects, as well as others, has been achieved by the features described herein.

The invention relates to a torque and angle of rotation detection system; comprising a rotor unit which is able to rotate about an axis of rotation; comprising a stator unit arranged in a stationary manner and separated from the rotor unit by an air gap that is radial with respect to the axis of rotation; wherein the rotor unit comprises strain gauges which detect a torque acting onto the rotor unit; wherein the rotor unit comprises a plurality of dipole magnets arranged spaced apart from each other; wherein the stator unit comprises a magnetic field sensor which measures the magnetic fields of the dipole magnets during rotation of the rotor unit; wherein the stator unit comprises a primary coil and the rotor unit comprises a secondary coil; wherein a primary electrical voltage in the primary coil generates a secondary electrical voltage in the secondary coil; wherein each of the dipole magnets has a remanence of more than or equal to 1,000 mT, preferably of more than or equal to 1,400 mT; and wherein the secondary coil comprises a plurality of ferrite elements.

According to the invention, the dipole magnets of the rotor assembly have a strong remanence. The remanence of the dipole magnets according to the invention is at least five times higher as compared to that of the magnetized ferrite powder/rubber mixture of the dipole magnets according to KiTorq. It is this strong remanence that enables the measurement of the magnetic fields of the dipole magnets by the magnetic field sensor of the stator unit to be carried out from a greater distance. Moreover, since the remanence is that strong it is not easily disturbed by external magnetic fields.

Ferrite elements consist of very pure iron-oxygen compounds pressed into uniform pellets at high pressure. Therefore, ferrite elements are characterized by containing a large proportion of magnetic material and are highly compacted. This is the reason why ferrite elements have a high permeability. Furthermore, ferrite elements achieve an improved efficiency of inductive coupling between the primary and secondary coils as compared to that of the iron powder/resin mixture according to KiTorq. Due to the improved efficiency, inductive coupling can occur over a greater distance.

Thus, the combination of dipole magnets having a strong remanence and ferrite elements in the secondary coil of the system according to the invention has the synergistic effect that it is possible to increase the radial air gap between the rotor unit and the stator unit and that it is further possible to increase the tolerance range for the permissible width of the radial air gap.

In addition, ferrite elements are inexpensive to purchase making the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the width of the radial air gap is more than/equal to 2.0 mm with a tolerance range for the radial air gap of +/−1.5 mm.

Here, the radial air gap is at least twice the size and its allowable radial air gap tolerance range is even three times as large compared to the torque and rotation angle sensing system of the prior art according to KiTorq.

In a presently preferred embodiment of the system, the rotor unit comprises a rotor body and a plurality of blind holes, which blind holes are provided on the outside of the rotor body, and wherein the ferrite elements are secured in the blind holes.

This securing of the ferrite elements in blind holes is easy to accomplish which makes the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the securing of the ferrite elements in the blind holes is achieved by a form-locking connection.

In a presently preferred embodiment of the system, each blind hole comprises an interior space, which interior space comprises at least one inner surface; wherein each ferrite element comprises at least one outer surface; and wherein the inner surface and the outer surface are machined to match one another in size and a mechanical contact of the inner and outer surfaces results in a form-locking connection.

The form-locking connection ensures that the ferrite elements do not become detached from the rotor body even under a high centrifugal force of 20000 minand more. This form-locking connection is easy to accomplish and makes the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the rotor unit comprises a coil winding, which coil winding is attached radially to the outside of the ferrite elements.

This attachment of the coil winding radially to the outside of the ferrite elements is also easy to accomplish which makes the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the dipole magnets are made of neodymium-iron-boron.

Dipole magnets made of neodymium-iron-boron are inexpensive to purchase which also makes the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the rotor unit comprises a rotor body and a groove, which groove is arranged radially in the outside of the rotor body; and wherein the dipole magnets are secured within the groove.

This groove is easily fabricated in the rotor body. In this way, the dipole magnets secured in the groove are arranged at substantially the same radial distance from the axis of rotation as the coil winding so that it is possible to cover the dipole magnets and coil winding by a rotor cover of simple design. Thus, the groove contributes to making the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the rotor unit comprises a rotor cover, which rotor cover is attached radially to the outside of the rotor unit.

In a presently preferred embodiment of the system, the rotor cover is attached to the rotor unit by a force-locking connection.

In a presently preferred embodiment of the system, the rotor cover is clamped onto the rotor unit.

In a presently preferred embodiment of the system, the rotor unit comprises a coil winding; and in that the rotor cover clamped onto the rotor unit completely covers the coil winding and the dipole magnets.

This rotor cover protects the dipole magnets and the coil winding from mechanical damage. This rotor cover can be easily attached to the rotor unit and makes the manufacture of the system cost-effective.

In a presently preferred embodiment of the system, the stator unit is arranged along the axis of rotation with an axial offset tolerance in the range of +/−1.0 mm relative to the rotor unit.

The axial offset tolerance corresponds to an axial degree of freedom when the stator unit is mounted adjacent to the rotor unit. The measurement of the magnetic fields of the dipole magnets by the magnetic field sensor is not disturbed when complying with this axial offset tolerance. Due to this axial degree of freedom the stator unit can be mounted adjacent to the rotor unit in an easy and quick manner.

In a presently preferred embodiment of the system, the magnetic field sensor generates a magnetic field signal for each magnetic field measured; wherein the stator unit comprises an evaluation unit, which evaluation unit executes an evaluation program; wherein the magnetic field sensor transmits the magnetic field signals to the evaluation unit; and wherein the evaluation program counts the magnetic field signals and multiplies them by the distance of the dipole magnets from each other to determine the angle of rotation that has been traveled by the rotor unit.

In a presently preferred embodiment of the system, the strain gauges generate measurement signals for a detected torque; wherein the rotor unit comprises a rotor antenna; wherein the strain gauges transmit the measurement signals to the rotor antenna; wherein the stator unit comprises a stator antenna and an evaluation unit, which evaluation unit executes an evaluation program; wherein the rotor antenna sends the measurement signals to the stator antenna; wherein the stator antenna transmits the measurement signals received from the rotor antenna to the evaluation unit; and wherein the evaluation program determines the torque that acts onto the rotor unit from the transmitted measurement signals.

shows a view of a portion of the torque and angle of rotation detection system that is designated generally by the numeral.is a representation of the view according toin section along line C-C.is an enlarged cross-sectional view of a portion of the systemas shown in.is an enlarged view of a portion of the rotor unitas shown in. In addition,is an enlarged cross-sectional view of a portion of the rotor unitaccording toalong line D-D. The same reference numerals designate the same features in the figures.

Systemis represented in a three-dimensional coordinate system comprising a rotational axis X, which is normal to the plane in whichlies, a horizontal axis Y, and a vertical axis Z. The three axes are perpendicular to each other.

Systemcomprises a rotor unit that is designated generally by the numeraland a stator unit that is designated generally by the numeral.

The rotor unitcomprises a rotor bodythat is hollow-cylindrical in shape. The rotor bodyis made of a mechanically resistant material such as steel, stainless steel, and the like. The rotor unitis designed as a flange which can be attached to any rotating component by means of a screw connection. The rotor unitis configured for rotational speeds of 20000 minand higher.

The stator unitis disposed in a stationary manner. As schematically shown in, the nearest surface of the statoris separated from the surface of the outermost peripheral edge of the rotor unitby a radial air gapwith respect to the axis of rotation X. The width of the radial air gapis more than/equal to 2.0 mm, and a tolerancefor the radial air gap is in the range of +/−1.5 mm. Regardless of this, as schematically shown in, there is an axial offset tolerancefor an offset relative to the rotor unitalong the axis of rotation X. The axial offset toleranceis in the range of +/−1.0 mm.

The rotor unitcomprises strain gaugesschematically shown in. The strain gaugescomprise a measurement grid and a bridge circuit. When an electrical voltage is applied to the measurement grid, the measurement grid exhibits an electrical resistance. The electrical resistance changes upon expansion or compression of the measurement grid, which change in electrical resistance generates measurement signals in the bridge circuit. The strain gaugesdetect torque in a dynamic manner generating up to 10,000 measurement signals per second at a sampling rate of up to 35 kSample. The measurement signals have a resolution of 24 bits. The strain gaugesdetect a maximum nominal torque of 100 Nm and more with an accuracy of within 0.05%.

As schematically shown in, the rotor unitfurther comprises a rotor antennaand the stator unitcomprises a stator antenna. The strain gaugesand the rotor antennaare electrically connected to each other by electrical connecting lines. The strain gaugestransmit the measurement signals to the rotor antennavia the electrical connecting lines. The measurement signals are transmitted from the rotor unitto the stator unitin a contactless manner. For this purpose, the rotor antennasends the measurement signals to the stator antenna. In a presently preferred embodiment, the transmission frequency of 13.56 MHz in the Industrial Scientific and Medical (ISM) band is used and a data transmission rate of up to 1.4 Mbitsecis achieved.